The preset invention relates to a semiconductor device and a manufacturing method for the same. In particular, the present invention is directed to an insulated gate field effect transistor (TFT) formed on an insulating surface, for example, a surface of an insulating substrate such as glass, or an insulating film such as silicon oxide formed on a silicon wafer. Also, the present invention is advantageous for the formation of an insulated gate field effect transistor, especially of an N-channel type, which is driven at a relatively high voltage. It is also to be understood that the present invention is further advantageous for the formation of a TFT on a glass substrate of which glass transition temperature (i.e. distortion point) is 750° C. or lower.
Moreover, the present invention is related to an active matrix of a liquid crystal device, a driving circuit of an image sensor or a three dimensional integrated circuit (hybrid IC) using the foregoing semiconductor devices.
In the prior art, TFTs have been known for driving an active-matrix type liquid crystal device or an image sensor or the like. Specifically, in place of an amorphous TFT using an amorphous silicon as an active layer, crystalline TFTs having a higher mobility are now being developed in order to increase driving speed. Moreover, TFTs having a high resistivity region (high resistivity drain) in an active region thereof have been proposed in order to further improve the device characteristics and to increase the capability of driving with a higher voltage. The “high resistivity region” or “high resistivity drain” in the present invention includes an impurity region (drain) having a higher resistivity, a lightly doped drain (LDD), and also an offset region where a gate electrode does not overlap an impurity region.
However, negative charges caused by hot carriers in an N-channel type TFT tend to be trapped in a portion of a gate insulating film close to a drain region so that the conductivity type of the high resistivity region shifts to p-type. As a result, the source/drain current is obstructed.
Also, it is necessary to use a photolithography technique to form a high resistivity region. This means that production yield and a uniformity of characteristics in the obtained TFTs can not be improved.